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Calcimator

Sight Triangle Calculator

Calculate clear sight triangle dimensions for intersection safety based on AASHTO guidelines, design speed, and intersection control type.

Inputs

mph
mph
sec
%

Results

Major Road Leg

152 ft

≈ 10 car lengths

Minor Road Leg

57 ft

≈ 10 adult heights

Clear Area4,323 sq ft
Stopping Sight Distance245 ft
Min. Setback20 ft
Driver Eye Height3.5 ft
Object Height3.5 ft
How to Use This Calculator
  1. Enter Intersection Control, Stop-Controlled, and Yield-Controlled.
  2. Set Uncontrolled, Major Road Design Speed, and Minor Road Speed.
  3. Adjust Lanes to Cross, Perception-Reaction Time as needed.
  4. Review Major Road Leg (ft) and Minor Road Leg (ft).
  5. Use Clear Area (sq ft) and Stopping Sight Distance (ft) to inform your decision.

How the result changes with Major Road Design Speed

Major Road Design SpeedMajor Road LegMinor Road Leg
2087 ft57 ft
33143 ft57 ft
48208 ft57 ft
60260 ft57 ft

What each input means

Intersection Control
Type of traffic control on the minor approach.
Major Road Design Speed
Design speed of the major (through) road.
Minor Road Speed
Speed of traffic on the minor (crossing) road.
Lanes to Cross
Number of travel lanes on the major road that must be crossed.
Perception-Reaction Time
Driver perception-reaction time. AASHTO default is 2.5 seconds.
Grade
Grade of the major road at the intersection. Negative = downhill approach.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Intersection Control = 1, Major Road Design Speed = 35, Minor Road Speed = 30, Lanes to Cross = 2 = 6 input(s) provided
  2. Calculate Major Road Leg
    Major Road Leg
    152 = 152
  3. Calculate Minor Road Leg
    Minor Road Leg
    57 = 57
  4. Calculate Clear Area
    Clear Area
    4323 = 4323
  5. Calculate Stopping Sight Distance
    Stopping Sight Distance
    245 = 245

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